Scanf

Objectives

1. Be able to write programs that employ scanf.

Notes

• scanf, like printf, takes
  • A format string, much like printf, but be careful
  • Addresses where data will be stored
• Like printf we need to
  • Save the base pointer, and set the stack pointer to be the base pointer.
  • Make sure that the stack is word aligned
    • Since I only push on 8 bit number, I need to subtract 8
  • Make sure that rdi holds the format string
  • Make sure that addresses are in rsi, rdx, rc, r8, r9, on the stack in reverse order
  • Call scanf
  • Unaligned the stack pointer if needed.
  • restore the base pointer
  • return
• Take a look at readExamp.asm
• Scanf will
  • Attempt to match the format string.
    • Literals must match exactly
    • Format variables will match like cin
    • Strings will be null terminated.
    • Read is probably better for strings, avoids buffer overflow, but we will work on that later.
  • It will return the number of input items matched
    • -1 on failure like eof